Protein phosphorylation is considered the main regulatory switch of the cell, controlling processes such as cell growth, proliferation, differentiation and survival. This control is performed by intricate signaling cascades;capable of changing proteins'activities and rapidly communicating messages from different extra cellular or internal cues to promote adequate cell readjustments. Deregulation of such networks and specifically of phosphorylation events has been shown to be the root cause for many diseases, and in particular constitutes the hallmark for most human cancers. Cancer is considered to be a genetic disease: DNA mutations, copy number aberrations, chromosomal rearrangements and modifications in DNA methylation contribute to the development and progression of human tumors. Genomic analysis of these abnormalities has shown its widespread occurrence in many cancers making it difficult to discriminate those mutations leading to cancer from those without functional effect. Interestingly, most of these defects seem to converge into aberrant protein phosphorylation patterns in a single or at most two signaling pathways simultaneously, thus studies of protein phosphorylation have the potential of revealing a common molecular signature in cancer from distinct mutation backgrounds. Novel mass spectrometry-based proteomics enables the analysis of protein phosphorylation en masse to offer a global picture of all phosphorylation events occurring in the cell. The goal of this proposal is to approach the study of signaling pathways in cancer using state-of-the-art proteomics technology, with special emphasis on the Ras/MAPK and PI3K/Akt pathways and their downstream effectors. This endeavor will be divided into three specific aims: 1) Development of technology for quantitative phosphoproteomics;2) Development and application of strategies to identify substrates of basophilic kinase substrates hyper- activated in cancer;3) Characterization of aberrant signaling pathways in breast cancer cell lines. The methodological aspects of this proposal, namely Aim 1 and part of Aim 2 will be completed during the mentored phase of the grant, relying on the extensive infrastructure within the Gygi lab. Aims 2 and 3 will be completed after the PI transitions to an independent tenure-track academic position. RELEVANCE: A broad characterization of signaling events in normal, kinase-activated and cancer cells will be invaluable to any researcher in signal transduction, cancer biology and translational research. Ras/MAPK and Akt/PI3K are of great interest in drug discovery programs. Results derived from this research proposal will highly impact the design of efficient therapies.